The present invention relates to a micro pump preferably having a small and thin structure.
In recent years, a micro pump driven by electrostatic force has been proposed in the field of micro machines which are produced by finely structuring a silicon substrate. Such a micro pump can be used either in a device embedded in a human body for injecting a very small amount of medicine thereinto or a small instrument for chemical analyses. It is known that such a micro pump is normally made of silicon, and it will be assumed that the micro pump is increasingly used in the field of medical treatment, chemical analyses and so on. In this case, it is preferable that the micro pump should have a small and thin structure, and in spite of these requirements, the micro pump ensures a greater amount of discharge (or a greater amount of displacement) for the fluid used.
In such a micro pump, however, it is very difficult to attain either a higher speed in pumping action or a greater amount of discharge (a greater magnitude of displacement) for a fluid.
In order to overcome such problems, the following pump has been proposed in Japanese Unexamined Patent Application Publication No. 2000-314381. FIG. 2 is a sectional view of the pump, which has a small and thin structure and at the same time provides a greater amount of discharge (a greater amount of displacement) for the fluid. The pump 110 comprises a casing 114, into which a fluid is supplied, a supply valve member 118 disposed so as to face the inside of the casing 114, a pump member 116, a discharge valve member 120, and a pump main body 112. A fluid channel is selectively formed in the inside of the casing 114 by the selective displacement of the supply valve member 118 the pump member 116, and the discharge valve member 120 in the approaching/departing direction, such that the flow of the fluid can be controlled by selectively forming the fluid channel.
In such a pump 110, however, the following problems exists. Since the displacement action of the pump member 116 resulted from the bending movement of a vibrating member 142, both the compression force and the magnitude of stroke in the discharge direction of the fluid were restricted, so that there was a limitation in manufacturing a pump having a small and thin structure in order to obtain a higher performance. The upper limit of the bending deformation of the vibrating member is determined by the toughness of the vibrating member 142, so that it is effective to decrease the thickness of the vibrating member 142, if the magnitudes of the bending deformation and the stroke can be increased in order to obtain a greater compression force. However, if so designed, the rigidity of the vibrating member 142 decreases and thus a high responsiveness is reduced. On the contrary, if the area of the vibrating member 142 can be increased, this causes an increase in the size of the vibrating member, hence making it impossible to provide a pump having a small and thin structure. On the other hand, an excellent responsiveness requires an increase of the rigidity. For this purpose, it is effective to increase the thickness of the vibrating member 142 in the pump 110. However, if so designed, the obtainable displacement is decreased and therefore the required compression force cannot be obtained. In other words, it was difficult to simultaneously attain both a greater compression force and a high responsiveness by the bending deformation of the vibrating member 142 in the pump 110.
Taking the above-mentioned problems into account, the object of the present invention is to provide a micro pump, which has a small and thin structure, and at the same time, ensures an increased amount of discharge (increased magnitude of displacement) and a high responsiveness. After many investigations were done regarding the structure for micro pumps, components for producing the displacement action and methods for producing the displacement action, it has been found that the above-mentioned object can be attained by the micro pump of the present invention, which is described below.
There is provided, in accordance with the invention, a micro pump having at least one pump member for conveying a fluid by the action of pressure, characterized in that, pump member comprises a pump unit which is formed from at least one actuator member for generating a pressure fluctuation and a fluid channel member in which a fluid flows. The actuator member is provided with a cell formed by disposing two side walls made of piezoelectric/electrostrictive elements or antiferrodielectric elements on a connecting plate, and a cover plate is positioned on the side walls and faces the connecting plate. The actuator member selectively forms a fluid channel and generates pressure fluctuation in the fluid channel member due to the displacement of the cell caused by expansion/contraction of the side walls.
In the pump unit, electrode layers are formed on both surfaces of the side walls in the actuator member, and the side walls are preferably expanded/contracted in the up/down direction in accordance with the driving electric field by applying a voltage to the electrode layers. For this purpose, the electric field for polarizing the piezoelectric/electrostrictive elements forming the side walls of the actuator member is aligned in the same direction as the driving electric field. Moreover, it is preferable that the state of crystalline grains on the surfaces of the side walls in the actuator member is that the crystalline grains suffering the fracture inside the grains are less than 1% and that the degree of profile of the surfaces of the cell in the actuator member is approximately 8 xcexcm or less.
In the pump unit, moreover, it is preferable that the ratio of the inside width to the height of the cell in the actuator member is approximately 1:2 to 1:40, and that the inside width of the cell in the actuator member is approximately less than 60 xcexcm. It is further preferable that the surface roughness Rt of the side walls in the actuator member is approximately 10 xcexcm or less.
In the actuator member of the pump unit, it is preferable that the connecting plate is made of piezoelectric/electrostrictive elements or antiferroelectric elements and joined to the side walls to form one body, and it is also preferable that the cover plate is made of piezoelectric/electrostrictive elements or antiferrodielectric elements and joined to the side walls to form one body.
In the present invention, for example, one of pump unit (A), pump unit (B) and pump unit (C) (which are each described below in detail) can be employed in the various embodiments. The pump unit (A) is constituted in such a manner that the cell in the actuator member is filled with a system fluid and another fluid, which is unsoluable in the system fluid flows in a fluid channel that is formed in advance in the fluid channel member. The cell is in communication with the fluid channel via a communicating hole, and the fluid channel has substantially the same size in the width direction as the diameter of the communicating hole, at least at the position where the communicating hole is in communication with to the fluid channel. The expansion/contraction (in the up/down direction) of the side walls forming the cell provides a change in the volume of the portion at which the system fluid stored in the cell is ejected from the communicating hole into the fluid channel, such that the fluid channel can be selectively formed.
The pump unit (B) is constituted in such a manner that the fluid channel is formed by a displacement transmitting member, at least a part of which is bonded to the cover plate of the cell in the actuator member, and a casing facing a part of the surface of the displacement transmitting member on the side opposite to the actuator member. The expansion/contraction of the side walls forming the cell provides an approaching/departing displacement of the displacement transmitting member relative to a part of the surfaces of the casing facing the displacement transmitting member, such that the fluid channel can be selectively formed.
In the pump unit (B), it is preferable that a communicating hole, through which the inside of the cell is communicated to the outside thereof, is formed. It is preferable that the fluid channel is closed when the displacement transmitting member comes into contact with the casing. Furthermore, it is preferable that a plurality of the actuator members are employed in accordance with the displacement transmitting members that form the fluid channel.
In the pump unit (B), when a plurality of the actuator members is employed in accordance with the displacement transmitting members that form the fluid channel, it is preferable that the ratio of the spacing between a cell and the adjacent cell to the height of the cell is approximately 1:2 to 1:40, and that the spacing between the cell and the adjacent cell is approximately 50 mm or less. Moreover, it is preferable that the inside width of the cell or the spacing between the cell and the adjacent cell has two different distances.
Regarding the actuator member in the above-mentioned pump unit (B), it is preferable that the outside of the cell is filled with the same material as the displacement transmitting member, and the actuator and the fluid channel member is unified into one body.
The pump unit (C) is constituted in such a manner that a fluid supply opening and a fluid discharge opening are formed in the cell of the actuator member, and a fluid channel including a supply channel portion and a discharge channel portion, in which a fluid flows, is formed in advance in the fluid channel member. The supply channel portion is in communication the fluid supply opening in the cell and the discharge channel is in communication with to the fluid discharge opening in the cell. The expansion/contraction of the side walls forming the cell provides a change in the volume of the cell and thus produces a pressure in the cell, such that the fluid channel can be selectively formed. In accordance with the invention, a micro pump including at least one pump member is provided, wherein the pump unit (A), the pump unit (B) and the pump unit (C), which are described above, are used as a pump member.
Moreover, in the micro pump according to the invention, wherein the micro pump includes the pump unit (A), the pump unit (B) and the pump unit (C) which are described above, it is desirable that pressure loss generating elements are each disposed on the supply side and the discharge side of the fluid channel. Assuming a pressure loss xcex94P1 when the fluid flows in the supply direction and a pressure loss xcex94P2 when the fluid flows in the direction opposite the supply direction at the pressure loss generating element on the supply side, and assuming a pressure loss xcex94P3 when the fluid flows in the discharge direction and a pressure loss xcex94P4 when the fluid flows in the direction opposite the discharge direction at the pressure loss generating element on the discharge side, the following two equations, xcex94P1 less than xcex94P4 and xcex94P2 greater than xcex94P3 are satisfied. In order to satisfy these conditions, the pressure loss generating element on the supply side has a tapered structure whose cross section continuously decreases in the supply direction of the fluid, and the pressure loss generating element on the discharge side has a tapered structure which continuously decreases in the discharge direction of the fluid. Moreover, each pressure loss generating element on the supply side and on the discharge side can be used check valve.
In the present invention, it is preferable that the pump members constituted by such pump units are used, and there is at least one set of serial connections in the pump members. It is also preferable that the pump members are used wherein there is an arbitrary combination of serial connection and/or parallel connection in the pump members. In this case, it is desirable that at least one set of two pump members connected in series among the pump members provides a phase difference in the pressure fluctuation arisen in the fluid channel member, thereby enabling the flow of the fluid to be controlled in the fluid channel member. Furthermore, when a plurality of pump members is used, it is preferable that the pump units in the pump members are of the same type.
It is also preferable that when a plurality of pump members are used, a valve member including one of the pump unit (A), the pump unit (B) and the pump unit (C) is interposed between at least one adjacent pump member. In this case, it is preferable that the pump unit in the pump member and the pump unit in the valve member are, for example, the pump unit (B), and therefore they are the same type pump unit.
In the present invention, it is preferable that at least one supply valve member comprising one of the pump unit (A), the pump unit (B) and the pump unit (C), which are described above, is disposed on the supply side of the pump member. In this case, it is preferable that the pump unit in the pump member and the pump unit in the supply valve member are the pump unit (C), and therefore they are the same type pump unit.
In addition, it is preferable that at least one discharge valve member comprising one of the pump unit (A), the pump unit (B) and the pump unit (C), which are described above, is disposed on the discharge side of the pump member. In this case, it is preferable that the pump unit in the pump member and the pump unit in the discharge valve member are the pump unit (A), and therefore they are the same type pump unit.
In the present invention, the actuator member in the pump unit, which is used as a pump member or a valve member, comprises a spacer plate made of piezoelectric/electrostrictive elements or antiferrodielectric elements in which a plurality of slits (A) is formed, a cover plate placed on one surface of said spacer plate for covering the slits (A) and a connecting plate placed on the other surface of the spacer plate for covering the slits (A), wherein a slit (B) passing through the cover plate and the spacer plate is formed between adjacent slits (A).
In accordance with the present invention, the following method for manufacturing a micro pump is provided. That is, the method for manufacturing a pump with a punch and a die, wherein cells are formed by two side walls made of piezoelectric/electrostrictive elements or antiferrodielectric elements disposed on a connecting plate and by a cover plate for covering the surface facing the connecting plate between the side walls, wherein the micro pump includes actuator members providing a displacement by the expansion/contraction of the side walls, wherein the method comprises the steps of: preparing a plurality of green sheets made of piezoelectric/electrostrictive material or antiferrodielectric material; performing a first substep for diecutting first slit apertures in a first green sheet with the punch, a second substep for raising the first green sheet in tight contact with a stripper, while maintaining the state in which the punch is not withdrawn from the first slit apertures and a third substep for raising the punch in such a manner that the front end of the punch is withdrawn slightly from the lowest part of the first green sheet raised; performing a fourth substep for diecutting second slit apertures in a second green sheet with the punch, a fifth substep for raising the second green sheet together with the first green sheet, while maintaining the state in which the punch is not withdrawn from the second slit apertures and a sixth substep for raising the punch in such a manner that the front end of the punch is withdrawn slightly from the lowest part of the second green sheet raised; subsequently laminating green sheets by repeating the fourth substep to the sixth substep to form a piezoelectric/electrostrictive element or antiferrodielectric element having a plurality of slits.